The invention relates to a method for detecting anomalies in a battery cell, and also to a short-circuit sensor system and a battery system which are designed for carrying out the method.
Present-day battery management systems monitor cell voltages, current intensities and cell temperatures with sampling rates of typically 20 to 50 Hz. With the aid of these variables and prior knowledge determined experimentally, for example on the basis of characteristic curves, a monitoring circuit is realized on the basis of a theoretical model of the battery cell. Typical variables determined by the battery management system (BMS) are the state of charge (SOC), the internal resistance and the general state (SOH, state of health) of the battery cells, in order for example to predict the available power and to provide framework stipulations for the operating parameters of the battery cells.
In lithium-ion batteries, the high quantity of chemical and electrical energy constitutes a potential risk. The chemical energy stored in the active materials of the cathode and the anode exceeds the stored electrical energy by a multiple. In this case, the release of the chemical energy by exothermic decomposition requires an activation energy in the form of heating. Depending on the materials used, the critical temperature is 150-200° C. The required temperature for initiating so-called thermal runaway may arise both as a result of external heating and as a result of internal heating of the battery cell. The external heating typically eludes an accurate prediction. The internal heating arises for example as a result of the release of electrical energy, as a result of electrical energy being converted into heat. In particular, this can be effected by internal electrical short circuits between cathode and anode which occur for example as a result of metallic particles, metal dendrites or electrical contact between the active materials. These processes are detected by battery management systems in the context of monitoring thermal runaway.
US 2013 012 2332 A1 describes a system comprising an integrated circuit, a pressure sensor and a communication device, which system can be mounted into a battery cell. The system serves for determining the SOC and the SOH of the battery cell. For detecting potential harmful reactions, in this case a rise in the cell internal pressure is determined, wherein a slow rise is interpreted as aging, while a fast rise is assessed as an indication of an acute hazard situation.
DE 10 2006 000 086 A1 discloses a rechargeable battery system comprising a rechargeable battery comprising a charging/discharging control section for controlling the battery in a control region, an anomaly detecting section for detecting anomalies and an anomaly processing section. The anomaly detecting section detects slight cell short-circuit anomalies of the battery on the basis of a block voltage of a battery monitoring unit.
DE 10 2008 062 656 A1 discloses a method for protecting a lithium-ion battery in a vehicle, wherein, for detecting a thermal and/or electrical overloading of the battery, parameters of the battery are automatically monitored, inter alia a current value, a voltage value, a temperature value and/or a cell internal pressure.
DE 10 2011 077 448 A1 discloses a method for estimating a state variable describing the state of an electrical energy store by means of a time-discreet comparison of operating variables with a mathematical model. Operating variables are the temperature, the load current and the terminal voltage.
It is an object of the invention to provide early detection of hazard situations caused by internal short circuits.